"On July 28, a commercial touring bus attempted to enter the U.S. through Detroit via the Ambassador Bridge," Chief Customs and Border Protection Officer Ken Hammond said in a statement to E! News.

"The tour bus, associated with musician Justin Bieber, was en route to a concert scheduled later Sunday night in Detroit. During the secondary inspection, a K-9 alerted to the presence of drugs and a subsequent search of the bus revealed marijuana and drug paraphernalia. Justin Bieber was not on the bus.

"Officers seized the marijuana and paraphernalia and issued a penalty to the driver. The bus and passengers were released without further incident," Hammond said.

Bieber's rep has not yet responded to a request for comment on the incident and the 19-year-old superstar himself has not given any indication via Twitter that anything went awry before the Detroit stop on his Believe Tour.

"Just talking about the last couple shows. Toronto and Detroit were real! Energy was next level. Thanks!" Bieber tweeted earlier today. His tour touches down in Newark, N.J., on Tuesday and then he plays Brooklyn's Barclays Center this Friday.

And that's the least of Bieber's travels. Before jetting to Toronto, he attended just-a-pal Selena Gomez's 21st birthday bash way over on the West Coast in Malibu on Saturday--and we're told that they left together and she spent the rest of the night at his Calabasas home.